In vitro antibacterial activity of porous TiO2-Ag composite layers against methicillin-resistant Staphylococcus aureus

In Vivo Prevention of Implant-Associated Infections Caused by Antibiotic-Resistant Bacteria through Biofunctionalization of Additively Manufactured Porous Titanium

Additively manufactured (AM) porous titanium implants may have an increased risk of implant-associated infection (IAI) due to their huge internal surfaces. However, the same surface, when biofunctionalized, can be used to prevent IAI. Here, we used a rat implant infection model to evaluate the biocompatibility and infection prevention performance of AM porous titanium against bioluminescent methicillin-resistant Staphylococcus aureus (MRSA). The specimens were biofunctionalized with Ag nanoparticles (NPs) using plasma electrolytic oxidation (PEO). Infection was initiated using either intramedullary injection in vivo or with in vitro inoculation of the implant prior to implantation. Nontreated (NT) implants were compared with PEO-treated implants with Ag NPs (PT-Ag), without Ag NPs (PT) and infection without an implant. After 7 days, the bacterial load and bone morphological changes were evaluated. When infection was initiated through in vivo injection, the presence of the implant did not enhance the infection, indicating that this technique may not assess the prevention but rather the treatment of IAIs. Following in vitro inoculation, the bacterial load on the implant and in the peri-implant bony tissue was reduced by over 90% for the PT-Ag implants compared to the PT and NT implants. All infected groups had enhanced osteomyelitis scores compared to the noninfected controls.

Titanium alloys with varying surface micro-area potential differences have antibacterial abilities and a favorable cellular response

OBJECTIVES

Surface micro-area potential difference (MAPD) can achieve bacteriostatic performance independent of metal ion dissolution. To study the influence of MAPD on antibacterial properties and the cellular response, Ti-Ag alloys with different surface potentials were designed and prepared by changing the preparation and heat treatment processes.

MATERIALS AND METHODS

Ti-Ag alloys (T4, T6, and S) were prepared by vacuum arc smelting, water quenching, and sintering. Cp-Ti was set as a control group in this work. The microstructures and surface potential distributions of the Ti-Ag alloys were analyzed by SEM and energy dispersive spectrometry. Plate counting and live/dead staining methods were used to evaluate the antibacterial properties of the alloys, and the mitochondrial function, ATP levels, and apoptosis were assessed in MC3T3-E1 cells to analyze the cellular response.

RESULTS

Due to the formation of the Ti-Ag intermetallic phase in the Ti-Ag alloys, Ti-Ag (T4) without the Ti-Ag phase had the lowest MAPD, Ti-Ag (T6) with a fine Ti2Ag phase had a moderate MAPD, and Ti-Ag (S) with a Ti-Ag intermetallic phase had the highest MAPD. The primary results demonstrated that the Ti-Ag samples with different MAPDs exhibited different bacteriostatic effects, ROS expression levels, and apoptosis-related protein expression levels in cells. The alloy with a high MAPD exhibited a strong antibacterial effect. A moderate MAPD stimulated cellular antioxidant regulation (GSH/GSSG) and downregulated the expression of intracellular ROS. MAPD could also promote the transformation of the inactive mitochondria to biologically active mitochondria by increasing the ΔΨm and reducing apoptosis.

CONCLUSION

The results here indicated that moderate MAPD not only had bacteriostatic effects but also promoted mitochondrial function and inhibited cell apoptosis, which provides a new strategy to improve the surface bioactivity of titanium alloys and a new idea for titanium alloy design.

CLINICAL RELEVANCE

There are some limitations of the mechanism of MAPD. However, researchers will become increasingly aware of the advantages and disadvantages of MAPD and MAPD might provide an affordable solution of peri-implantitis.

Food-grade titanium dioxide can affect microbiota physiology, adhesion capability, and interbacterial interactions: A study onL. rhamnosus and E. faecium

Food-grade titanium dioxide (TiO₂-FG) is a widespread metal oxide used in the food industries. Recently, the European Food Safety Authority concluded that TiO₂-FG cannot be considered safe for consumption due to its genotoxicity; however, its effect on the gut microbiota has not yet been completely unraveled. We studied the effects of TiO₂-FG (0.125 mg/mL) on Lactobacillus rhamnosus GG (LGG) and Enterococcus faecium NCIMB10415 (Ent), in particular some physiological and phenotypic traits (growth kinetics, bile salts, and ampicillin resistance) and their interactions with the host (auto-aggregation, biofilm formation, and adhesion on Caco-2/TC7 monolayers) and other gut microorganisms (antimicrobial activity towards pathogens). The results obtained revealed that TiO₂-FG alters both LGG and Ent growth and lowers bile resistance (62 and 34.5%, respectively) and adhesion on Caco-2/TC7 monolayers (34.8 and 14.16%, respectively). The other outcomes were strictly species-specific: Ent showed a lower ampicillin sensitivity (14.48%) and auto-aggregation (38.1%), while LGG showed a reduced biofilm formation (37%) and antimicrobial activity towards Staphylococcus aureus (35.73%). Overall, these results suggest an adverse effect of TiO₂-FG on both the endogenous and exogenously administered probiotics, contributing to the argument against using TiO₂-FG as a food additive.

The race for the optimal antimicrobial surface: perspectives and challenges related to plasma electrolytic oxidation coating for titanium-based implants

Plasma electrolytic oxidation (PEO) is a low-cost, structurally reliable, and environmentally friendly surface modification method for orthopedic and dental implants. This technique is successful for the formation of porous, corrosion-resistant, and bioactive coatings, besides introducing antimicrobial compounds easily. Given the increase in implant-related infections, antimicrobial PEO-treated surfaces have been widely proposed to surmount this public health concern. This review comprehensively discusses antimicrobial implant surfaces currently produced by PEO in terms of their in vitro and in vivo microbiological and biological properties. We present a critical [part I] and evidence-based [part II] review about the plethora of antimicrobial PEO-treated surfaces. The mechanism of microbial accumulation on implanted devices and the principles of PEO technology to ensure antimicrobial functionalization by one- or multi-step processes are outlined. Our systematic literature search showed that particular focus has been placed on the metallic and semi-metallic elements incorporated into PEO surfaces to facilitate antimicrobial properties, which are often dose-dependent, without leading to cytotoxicity in vitro. Meanwhile, there are concerns over the biocompatibility of PEO and its long-term antimicrobial effects in animal models. We clearly highlight the importance of using clinically relevant infection models and in vivo long-term assessments to guarantee the rational design of antimicrobial PEO-treated surfaces to identify the 'finish line' in the race for antimicrobial implant surfaces.

Inhibition of Phytopathogenic and Beneficial Fungi Applying Silver Nanoparticles In Vitro

In the current research, our work measured the effect of silver nanoparticles (AgNP) synthesized from Larrea tridentata (Sessé and Moc. ex DC.) on the mycelial growth and morphological changes in mycelia from different phytopathogenic and beneficial fungi. The assessment was conducted in Petri dishes, with Potato-Dextrose-Agar (PDA) as the culture medium; the AgNP concentrations used were 0, 60, 90, and 120 ppm. Alternaria solani and Botrytis cinerea showed the maximum growth inhibition at 60 ppm (70.76% and 51.75%). Likewise, Macrophomina spp. required 120 ppm of AgNP to achieve 65.43%, while Fusarium oxisporum was less susceptible, reaching an inhibition of 39.04% at the same concentration. The effect of silver nanoparticles was inconspicuous in Pestalotia spp., Colletotrichum gloesporoides, Phytophthora cinnamomi, Beauveria bassiana, Metarhizium anisopliae, and Trichoderma viridae fungi. The changes observed in the morphology of the fungi treated with nanoparticles were loss of definition, turgidity, and constriction sites that cause aggregations of mycelium, dispersion of spores, and reduced mycelium growth. AgNP could be a sustainable alternative to managing diseases caused by Alternaria solani and Macrophomina spp.

Preventing Antibiotic-Resistant Infections: Additively Manufactured Porous Ti6Al4V Biofunctionalized with Ag and Fe Nanoparticles

Implant-associated infections are highly challenging to treat, particularly with the emergence of multidrug-resistant microbials. Effective preventive action is desired to be at the implant site. Surface biofunctionalization of implants through Ag-doping has demonstrated potent antibacterial results. However, it may adversely affect bone regeneration at high doses. Benefiting from the potential synergistic effects, combining Ag with other antibacterial agents can substantially decrease the required Ag concentration. To date, no study has been performed on immobilizing both Ag and Fe nanoparticles (NPs) on the surface of additively manufactured porous titanium. We additively manufactured porous titanium and biofunctionalized its surface with plasma electrolytic oxidation using a Ca/P-based electrolyte containing Fe NPs, Ag NPs, and the combinations. The specimen’s surface morphology featured porous TiO2 bearing Ag and Fe NPs. During immersion, Ag and Fe ions were released for up to 28 days. Antibacterial assays against methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa showed that the specimens containing Ag NPs and Ag/Fe NPs exhibit bactericidal activity. The Ag and Fe NPs worked synergistically, even when Ag was reduced by up to three times. The biofunctionalized scaffold reduced Ag and Fe NPs, improving preosteoblasts proliferation and Ca-sensing receptor activation. In conclusion, surface biofunctionalization of porous titanium with Ag and Fe NPs is a promising strategy to prevent implant-associated infections and allow bone regeneration and, therefore, should be developed for clinical application.

Antibacterial Ti-Cu implants: A critical review on mechanisms of action

Titanium (Ti) has been widely used for manufacturing of bone implants because of its mechanical properties, biological compatibility, and favorable corrosion resistance in biological environments. However, Ti implants are prone to infection (peri-implantitis) by bacteria which in extreme cases necessitate painful and costly revision surgeries. An emerging, viable solution for this problem is to use copper (Cu) as an antibacterial agent in the alloying system of Ti. The addition of copper provides excellent antibacterial activities, but the underpinning mechanisms are still obscure. This review sheds light on such mechanisms and reviews how incorporation of Cu can render Ti–Cu implants with antibacterial activity. The review first discusses the fundamentals of interactions between bacteria and implanted surfaces followed by an overview of the most common engineering strategies utilized to endow an implant with antibacterial activity. The underlying mechanisms for antibacterial activity of Ti–Cu implants are then discussed in detail. Special attention is paid to contact killing mechanisms because the misinterpretation of this mechanism is the root of discrepancies in the literature.

Synthesis and Investigation of Antibacterial Activity of Thin Films Based on TiO2-Ag and SiO2-Ag with Potential Applications in Medical Environment

Multiple antibiotic resistance has now become a major obstacle to the treatment of infectious diseases. In this context, the application of nanotechnology in medicine is a promising alternative for the prevention of infections with multidrug-resistant germs. The use of silver as a powerful antibacterial agent has attracted much interest. TiO2 and SiO2 thin films enhanced with Ag particles have been developed with the aim of maintaining the transparency of the polymer films. Antibacterial activity was evaluated for a Gram-negative species-Escherichia coli-in concentrations of 105 and 104 CFU/mL in different conditions-activation by UV irradiation, single layer and double layer. Increased antibacterial efficacy of TiO2-deposited foil was found for the tests that had been exposed to UV activation. In the case of bilayer tests, the efficiency was higher compared to those in a single layer, as the contact surface between the films and the bacterial suspension increased. Films can be used as a potential method to limit bacterial growth on hospital surfaces, such as telephone screens and medical equipment, given their optimized characteristics and proven antibacterial efficacy.

Antimicrobial Efficacy and Spectrum of Phosphorous-Fluorine Co-Doped TiO2 Nanoparticles on the Foodborne Pathogenic Bacteria Campylobacter jejuni, Salmonella Typhimurium, Enterohaemorrhagic E. coli, Yersinia enterocolitica, Shewanella putrefaciens, Listeria monocytogenes and Staphylococcus aureus

Contamination of meats and meat products with foodborne pathogenic bacteria raises serious safety issues in the food industry. The antibacterial activities of phosphorous-fluorine co-doped TiO₂ nanoparticles (PF-TiO₂) were investigated against seven foodborne pathogenic bacteria: Campylobacter jejuni, Salmonella Typhimurium, Enterohaemorrhagic E. coli, Yersinia enterocolitica, Shewanella putrefaciens, Listeria monocytogenes and Staphylococcus aureus. PF-TiO₂ NPs were synthesized hydrothermally at 250 °C for 1, 3, 6 or 12 h, and then tested at three different concentrations (500 μg/mL, 100 μg/mL, 20 μg/mL) for the inactivation of foodborne bacteria under UVA irradiation, daylight exposure or dark conditions. The antibacterial efficacies were compared after 30 min of exposure to light. Distinct differences in the antibacterial activities of the PF-TiO₂ NPs, and the susceptibilities of tested foodborne pathogenic bacterium species were found. PF-TiO₂/3 h and PF-TiO₂/6 h showed the highest antibacterial activity by decreasing the living bacterial cell number from ~10⁶ by ~5 log (L. monocytogenes), ~4 log (EHEC), ~3 log (Y. enterolcolitca, S. putrefaciens) and ~2.5 log (S. aureus), along with complete eradication of C. jejuni and S. Typhimurium. Efficacy of PF-TiO₂/1 h and PF-TiO₂/12 h NPs was lower, typically causing a ~2–4 log decrease in colony forming units depending on the tested bacterium while the effect of PF-TiO₂/0 h was comparable to P25 TiO₂, a commercial TiO₂ with high photocatalytic activity. Our results show that PF-co-doping of TiO₂ NPs enhanced the antibacterial action against foodborne pathogenic bacteria and are potential candidates for use in the food industry as active surface components, potentially contributing to the production of meats that are safe for consumption.

Comparative antibacterial activity of 2D materials coated on porous-titania

Plasma electrolytic oxidation (PEO) is a well-established technique for the treatment of titanium-based materials. The formed titania-PEO surface can improve the osseointegration properties of titanium implants. Nevertheless, it can not address bacterial infection problems associated with bone implants. Recently, 2-dimensional (2D) materials such as graphene oxide (GO), MXene, and hexagonal boron nitride (hBN) have received considerable attention for surface modifications showing their antibacterial properties. In this paper, a comparative study on the effect of partial deposition of these three materials over PEO titania substrates on the antibacterial efficiency and bioactivity is presented. Their partial deposition through drop-casting instead of continuous film coating is propsed to simultaneously address both antibacterial and osseointegration abilities. Our results demonstrate the dose-dependent nature of the deposited antibacterial agent on the PEO substrate. GO-PEO and MXene-PEO samples showed the highest antibacterial activity with 70 (±2) % and 97 (±0.5) % inactivation of S. aureus colonies in the low concentration group, respectively. Furthermore, only samples in the higher concentration group were effective against E. coli bacteria with 18 (±2) % and 17 (±4) % decrease in numbers of colonies for hBN-PEO and GO-PEO samples, respectively. Moreover, all antibacterial samples demonstrated acceptable bioactivity and good biocompatibility, making them a considerable candidates for the next generation of antibacterial titanium implants.

Antibacterial Titanium Implants Biofunctionalized by Plasma Electrolytic Oxidation with Silver, Zinc, and Copper: A Systematic Review

Patients receiving orthopedic implants are at risk of implant-associated infections (IAI). A growing number of antibiotic-resistant bacteria threaten to hamper the treatment of IAI. The focus has, therefore, shifted towards the development of implants with intrinsic antibacterial activity to prevent the occurrence of infection. The use of Ag, Cu, and Zn has gained momentum as these elements display strong antibacterial behavior and target a wide spectrum of bacteria. In order to incorporate these elements into the surface of titanium-based bone implants, plasma electrolytic oxidation (PEO) has been widely investigated as a single-step process that can biofunctionalize these (highly porous) implant surfaces. Here, we present a systematic review of the studies published between 2009 until 2020 on the biomaterial properties, antibacterial behavior, and biocompatibility of titanium implants biofunctionalized by PEO using Ag, Cu, and Zn. We observed that 100% of surfaces bearing Ag (Ag-surfaces), 93% of surfaces bearing Cu (Cu-surfaces), 73% of surfaces bearing Zn (Zn-surfaces), and 100% of surfaces combining Ag, Cu, and Zn resulted in a significant (i.e., >50%) reduction of bacterial load, while 13% of Ag-surfaces, 10% of Cu-surfaces, and none of Zn or combined Ag, Cu, and Zn surfaces reported cytotoxicity against osteoblasts, stem cells, and immune cells. A majority of the studies investigated the antibacterial activity against S. aureus. Important areas for future research include the biofunctionalization of additively manufactured porous implants and surfaces combining Ag, Cu, and Zn. Furthermore, the antibacterial activity of such implants should be determined in assays focused on prevention, rather than the treatment of IAIs. These implants should be tested using appropriate in vivo bone infection models capable of assessing whether titanium implants biofunctionalized by PEO with Ag, Cu, and Zn can contribute to protect patients against IAI.

Self-defending additively manufactured bone implants bearing silver and copper nanoparticles

Effective preventive measures against implant-associated infection (IAI) are desperately needed. Therefore, the development of self-defending implants with intrinsic antibacterial properties has gained significant momentum. Biomaterials biofunctionalized with silver (Ag) have resulted in effective antibacterial biomaterials, yet regularly induce cytotoxicity. In this study, the use of both Ag and copper (Cu) nanoparticles (NPs) on TiO2 surfaces was investigated to generate antibacterial and osteoconductive biomaterials. Hence, additively manufactured Ti-6Al-4V volume-porous implants were biofunctionalized with plasma electrolytic oxidation (PEO) through the incorporation of varying ratios of Ag and/or Cu NPs in the TiO2 layer covering the implant surface. For all experimental groups, the surface morphology, chemical composition, ion release profile, generation of reactive ion species, antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) in vitro and ex vivo, as well as the response of pre-osteoblastic MC3T3-E1 cells in metabolic activity and differentiation assays were determined. PEO biofunctionalization resulted in rough and highly porous surfaces that released Ag and Cu ions for 28 days and generated hydroxyl as well as methyl radicals. A strong synergistic bactericidal behavior between Ag and Cu ions was detected, which allowed to decrease the concentration of Ag ions by 10-fold, while maintaining the same level of antibacterial activity. Antibacterial agar diffusion and quantitative assays indicated strong antibacterial activity in vitro for the implants containing Ag and Ag/Cu, while no antibacterial activity was observed for implants bearing only Cu NPs. Moreover, the biofunctionalized implants with ratios of up to 75% Ag and 25% Cu NP totally eradicated all bacteria in an ex vivo model using murine femora. Meanwhile, the biofunctionalized implants did not show any signs of cytotoxicity, while implants bearing only Cu NPs improved the metabolic activity after 7 and 11 days. The biomaterials developed here, therefore, exploit the synergistic behavior of Ag and Cu to simultaneously offer strong antibacterial behavior while fully mitigating the cytotoxicity of Ag against mammalian cells.

Antimicrobial Properties of the Ag, Cu Nanoparticle System

Microbes, including bacteria and fungi, easily form stable biofilms on many surfaces. Such biofilms have high resistance to antibiotics, and cause nosocomial and postoperative infections. The antimicrobial and antiviral behaviors of Ag and Cu nanoparticles (NPs) are well known, and possible mechanisms for their actions, such as released ions, reactive oxygen species (ROS), contact killing, the immunostimulatory effect, and others have been proposed. Ag and Cu NPs, and their derivative NPs, have different antimicrobial capacities and cytotoxicities. Factors, such as size, shape and surface treatment, influence their antimicrobial activities. The biomedical application of antimicrobial Ag and Cu NPs involves coating onto substrates, including textiles, polymers, ceramics, and metals. Because Ag and Cu are immiscible, synthetic AgCu nanoalloys have different microstructures, which impact their antimicrobial effects. When mixed, the combination of Ag and Cu NPs act synergistically, offering substantially enhanced antimicrobial behavior. However, when alloyed in Ag-Cu NPs, the antimicrobial behavior is even more enhanced. The reason for this enhancement is unclear. Here, we discuss these results and the possible behavior mechanisms that underlie them.

Smart Titanium Coating Composed of Antibiotic Conjugated Peptides as an Infection-Responsive Antibacterial Agent

Antibacterial coating is rapidly emerging as a pivotal strategy for mitigating spread of bacterial pathogens. However, many challenges still need to be overcome in order to develop a smart coating that can achieve on-demand antibacterial effects. In this study, a Staphylococcus aureus (S. aureus) sensitive peptide sequence is designed, and an antibiotic is then conjugated with this tailor-made peptide. The antibiotic-peptide conjugate is then linked to the surface of a titanium implant, where the peptide can be recognized and cleaved by an enzyme secreted by S. aureus. This allows for the release of antibiotics in the presence of S. aureus, thus achieving delivery of an antibacterial specifically when an infection occurs.

Antimicrobial Properties of MgO Nanostructures on Magnesium Substrates

Magnesium (Mg) and its alloys have attracted increasing attention in recent years as medical implants for repairing musculoskeletal injuries because of their promising mechanical and biological properties. However, rapid degradation of Mg and its alloys in physiological fluids limited their clinical translation because the accumulation of hydrogen (H2) gas and fast release of OH- ions could adversely affect the healing process. Moreover, infection is a major concern for internally implanted devices because it could lead to biofilm formation, prevent host cell attachment on the implants, and interfere osseointegration, resulting in implant failure or other complications. Fabricating nanostructured magnesium oxide (MgO) on magnesium (Mg) substrates is promising in addressing both problems because it could slow down the degradation process and improve the antimicrobial activity. In this study, nanostructured MgO layers were created on Mg substrates using two different surface treatment techniques, i.e., anodization and electrophoretic deposition (EPD), and cultured with Staphylococcus aureus in vitro to determine their antimicrobial properties. At the end of the 24-h bacterial culture, the nanostructured MgO layers on Mg prepared by anodization or EPD both showed significant bactericidal effect against S. aureus. Thus, nanostructured MgO layers on Mg are promising for reducing implant-related infections and complications and should be further explored for clinical translation toward antimicrobial biodegradable implants.

Antimicrobial Prosthetic Surfaces in the Oral Cavity-A Perspective on Creative Approaches

Replacement of missing teeth is an essential component of comprehensive dental care for patients suffering of edentulism. A popular option is implant-supported restorations. However, implant surfaces can become colonized with polymicrobial biofilms containing Candida species that may compromise peri-implant health. To prevent this, implant components may be treated with a variety of coatings to create surfaces that either repel the attachment of viable microorganisms or kill microorganisms on contact. These coatings may consist of nanoparticles of pure elements (more commonly silver, copper, and zinc), sanitizing agents and disinfectants (quaternary ammonium ions and chlorhexidine), antibiotics (cefalotin, vancomycin, and gentamicin), or antimicrobial peptides (AMPs). AMPs in bioactive coatings have a number of advantages. They elicit a protective action against pathogens, inhibit the formation of biofilms, are less toxic to host tissues, and do not prompt inflammatory responses. Furthermore, many of these coatings may involve unique delivery systems to direct their antimicrobial capacity against pathogens, but not commensals. Coatings may also contain multiple antimicrobial substances to widen antimicrobial activity across multiple microbial species. Here, we compiled relevant information about a variety of creative approaches used to generate antimicrobial prosthetic surfaces in the oral cavity with the purpose of facilitating implant integration and peri-implant tissue health.

Phosphate Porous Coatings Enriched with Selected Elements via PEO Treatment on Titanium and Its Alloys: A Review

This paper shows that the subject of porous coatings fabrication by Plasma Electrolytic Oxidation (PEO), known also as Micro Arc Oxidation (MAO), is still current, inter alia because metals and alloys, which can be treated by the PEO method, for example, titanium, niobium, tantalum and their alloys, are increasingly available for sale. On the international market, apart from scientific works/activity developed at universities, scientific research on the PEO coatings is also underway in companies such as Keronite (Great Britain), Magoxid-Coat (Germany), Mofratech (France), Machaon (Russia), as well as CeraFuse, Tagnite, Microplasmic (USA). In addition, it should be noted that the development of the space industry and implantology will force the production of trouble-free micro- and macro-machines with very high durability. Another aspect in favor of this technique is the rate of part treatment, which does not exceed several dozen minutes, and usually only lasts a few minutes. Another advantage is functionalization of fabricated surface through thermal or hydrothermal modification of fabricated coatings, or other methods (Physical vapor deposition (PVD), chemical vapor deposition (CVD), sol-gel), including also reoxidation by PEO treatment in another electrolyte. In the following chapters, coatings obtained both in aqueous solutions and electrolytes based on orthophosphoric acid will be presented; therein, dependent on the PEO treatment and the electrolyte used, they are characterized by different properties associated with their subsequent use. The possibilities for using coatings produced by means of plasma electrolytic oxidation are very wide, beginning from various types of catalysts, gas sensors, to biocompatible and antibacterial coatings, as well as hard wear coatings used in machine parts, among others, used in the aviation and aerospace industries.

Immunomodulation of surface biofunctionalized 3D printed porous titanium implants

Additive manufacturing (AM) techniques have provided many opportunities for the rational design of porous metallic biomaterials with complex and precisely controlled topologies that give rise to unprecedented combinations of mechanical, physical, and biological properties. These favorable properties can be enhanced by surface biofunctionalization to enable full tissue regeneration and minimize the risk of implant-associated infections (IAIs). There is, however, an increasing need to investigate the immune responses triggered by surface biofunctionalized AM porous metals. Here, we studied the immunomodulatory effects of AM porous titanium (Ti-6Al-4V) printed using selective laser melting, and of two additional groups consisting of AM implants surface biofunctionalized using plasma electrolytic oxidation (PEO) with/without silver nanoparticles. The responses of human primary macrophages and human mesenchymal stromal cells (hMSCs) were studied in terms of cell viability, cell morphology and biomarkers of macrophage polarization. Non-treated AM porous titanium triggered a strong pro-inflammatory response in macrophages, albeit combined with signs of anti-inflammatory effects. The PEO treatment of AM porous titanium implants showed a higher potential to induce polarization towards a pro-repair macrophage phenotype. We detected no cytotoxicity against hMSCs in any of the groups. However, the incorporation of silver nanoparticles resulted in strong cytotoxicity against attached macrophages. The results of this study indicate the potential immunomodulatory effects of the AM porous titanium enhanced with PEO treatment, and point towards caution and further research when using silver nanoparticles for preventing IAIs.

Biofunctionalization of selective laser melted porous titanium using silver and zinc nanoparticles to prevent infections by antibiotic-resistant bacteria

Antibiotic-resistant bacteria are frequently involved in implant-associated infections (IAIs), making the treatment of these infections even more challenging. Therefore, multifunctional implant surfaces that simultaneously possess antibacterial activity and induce osseointegration are highly desired in order to prevent IAIs. The incorporation of multiple inorganic antibacterial agents onto the implant surface may aid in generating synergistic antibacterial behavior against a wide microbial spectrum while reducing the occurrence of bacterial resistance. In this study, porous titanium implants synthesized by selective laser melting (SLM) were biofunctionalized with plasma electrolytic oxidation (PEO) using electrolytes based on Ca/P species as well as silver and zinc nanoparticles in ratios from 0 to 100% that were tightly embedded into the growing titanium oxide layer. After the surface bio-functionalization process, silver and zinc ions were released from the implant surfaces for at least 28 days resulting in antibacterial leaching activity against methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, the biofunctionalized implants generated reactive oxygen species, thereby contributing to antibacterial contact-killing. While implant surfaces containing up to 75% silver and 25% zinc nanoparticles fully eradicated both adherent and planktonic bacteria in vitro as well as in an ex vivo experiment performed using murine femora, solely zinc-bearing surfaces did not. The minimum inhibitory and bactericidal concentrations determined for different combinations of both types of ions confirmed the presence of a strong synergistic antibacterial behavior, which could be exploited to reduce the amount of required silver ions by two orders of magnitude (i.e., 120 folds). At the same time, the zinc bearing surfaces enhanced the metabolic activity of pre-osteoblasts after 3, 7, and 11 days. Altogether, implant biofunctionalization by PEO with silver and zinc nanoparticles is a fruitful strategy for the synthesis of multifunctional surfaces on orthopedic implants and the prevention of IAIs caused by antibiotic-resistant bacteria. STATEMENT OF SIGNIFICANCE: Implant-associated infections are becoming increasingly challenging to treat due to growing antibiotic resistance against antibiotics. Here, we propose an alternative approach where silver and zinc nanoparticles are simultaneously used for the biofunctionalization of rationally designed additively manufactured porous titanium. This combination of porous design and tailored surface treatment allows us to reduce the amount of required silver nanoparticles by two orders of magnitude, fully eradicate antibiotic-resistant bacteria, and enhance the osteogenic behavior of pre-osteoblasts. We demonstrate that the resulting implants display antibacterial activity in vitro and ex vivo against methicillin-resistant Staphylococcus aureus.

ROS induced bactericidal activity of amorphous Zn-doped titanium oxide coatings and enhanced osseointegration in bacteria-infected rat tibias

Titanium-based endosseous implants with high antibacterial and osseointegration activities are extremely required in clinics. To achieve this line, herein the doped coatings with three kinds of Zn doses were micro-arc oxidized (MAOed) on Ti. They were examined to reveal a bilayered structure, in which the outer layer consisted completely of the amorphism comprising elements of Ti, O and Zn with Zn doped in the form of weaken Zn-O bonds, and the underlying layer was partially crystallized with nanocrystalline TiO₂ and Zn₂TiO₄ to embed an amorphous matrix. While the Zn doped doses of the surface amorphous layers increased with elevating the MAOed voltages, the weaken Zn-O bonds in the amorphism were identified to act as both the contributor of Zn²⁺ controllable release and the generator of reactive oxide species (ROS) on the coatings. The enhanced HO• and O₂^-• formation on the elevated voltage MAOed coatings caused serious break of the cell walls and plasma membranes of S. aureus. In parallel, the enhanced Zn²⁺ release and extracellular H₂O₂ formation led to the enhanced intracellular ROS level of S. aureus, further aggravating the damage of plasma membrane, resulting in bacteria death. On contrary to the overdose of Zn doped coating, the moderate doses of Zn doped coatings did not induce additional intracellular ROS and attenuate viability and proliferation of osteoblasts in vitro, and promoted osseointegration in both S. aureus-uninfected and infected rat tibias, which ascribed to the strong antibacterial activity and un-attenuated cell function of the coatings in the infected case. STATEMENT OF SIGNIFICANCE: (1) The Zn-doped coatings revealed a bilayered structure of the surface layer comprising the Ti, O and Zn constructed amorphism with Zn in the form of weaken Zn-O bonds, and the underlying layer comprising nanocrystalline TiO₂ and Zn₂TiO₄ to embed amorphous matrix. (2) The weaken Zn-O bonds in the amorphism were identified to act as both the contributor of Zn²⁺ controllable release and the generator of ROS on the coatings. (3) The enhanced Zn²⁺ release and ROS formation on the coatings killed S. aureus by inducing serious break of their cell walls and plasma membranes. This effect in combination of un-attenuated osteoblast proliferation endowed the moderate Zn doped coatings with enhanced osseointegration in S. aureus-infected rat tibias.

Investigation of antibacterial effect of copper introduced titanium surface by electrochemical treatment against facultative anaerobic bacteria

This study investigated the efficacy of copper (Cu) as an antibacterial element incorporated on titanium (Ti) surface by electrochemical treatment. Cu was incorporated onto Ti surface by micro-arc oxidation (MAO). A small amount of Cu was incorporated into the oxide layer and was found to be in oxidized states. Cu-incorporated samples exhibited no-harmful effect on the proliferation of osteoblastlike cells. Moreover, the difference in antibacterial property between fresh and incubated samples was evaluated using gram-positive and gram-negative facultative anaerobic bacteria. The specific antibacterial property of Cu incorporated into the Ti surface were confirmed. The antibacterial property prolonged upon immersion in physiological saline for 28 days. In other words, MAO-treated Ti containing Cu in this study is expected to achieve long-term antibacterial property in practical usage.

Preparation, Characteristics, and Application of Bifunctional TiO2 Sheets

TiO₂ is a high-reflectance material for preparing sheets during dry reagent chemical tests in detail. In this study, bifunctional TiO₂ sheets with diffusive and reflective properties were prepared using TiO₂ microspheres (particle size 2–3 µm) and cellulose acetate (CA). Factors such as the CA dosage, water content, mixing time, and the choice of surfactant were investigated. The structure and properties of the bifunctional TiO₂ sheets were characterized by thermogravimetry and differential thermal analysis (TG-DAT), scanning electron microscopy (SEM), dynamic contact angle test and reflectance spectroscopy. By studying the above experimental results, it was concluded that the most optimal preparation conditions for preparing the bi-functional TiO₂ sheets under natural drying conditions were as follows: the mass ratio of CA to TiO₂ microspheres was 0.05:1; Triton-100 was used to improve the diffusion performance of the bifunctional sheets, after mixing for 5 h and coating. The light reflectivity of the bifunctional TiO₂ sheets in the 420 to 800 nm range was higher than 90%. Serum diffused in the bifunctional TiO₂ sheets reacted in the reagent sheets and formed uniform colorful spots. Considering the repeatability of spot proportion and light reflectivity, the sheet offered a uniform serum diffusion and good repeatability. So, the bifunctional TiO₂ sheets are nominated as a promising material for dry chemical diagnostic reagents.

Ag Nanoparticle-Decorated Oxide Coatings Formed via Plasma Electrolytic Oxidation on ZrNb Alloy

Plasma electrolytic oxidation (PEO) can provide an ideal surface for osteogenic cell attachment and proliferation with further successful osteointegration. However, the same surface is attractive for bacteria due to similar mechanisms of adhesion in prokaryotic and eukaryotic cells. This issue requires the application of additional surface treatments for effective prevention of postoperative infectious complications. In the present work, ZrNb alloy was treated in a Ca-P solution with Ag nanoparticles (AgNPs) for the development of a new oxide layer that hosted osteogenic cells and prevented bacterial adhesion. For the PEO, 0.5 M Ca(H₂PO₂)₂ solution with 264 mg L⁻¹ of round-shaped AgNPs was used. Scanning electron microscopy with energy-dispersive x-ray and x-ray photoelectron spectroscopy were used for morphology and chemical analysis of the obtained samples; the SBF immersion test, bacteria adhesion test, and osteoblast cell culture were used for biological investigation. PEO in a Ca-P bath with AgNPs provides the formation of a mesoporous oxide layer that supports osteoblast cell adhesion and proliferation. Additionally, the obtained surface with incorporated Ag prevents bacterial adhesion in the first 6 h after immersion in a pathogen suspension, which can be an effective approach to prevent infectious complications after implantation.

Anti-Methicillin-Resistant Staphylococcus aureus Nanoantibiotics

Nanoparticle-based antibiotic constructs have become a popular area of investigation in the biomedical sciences. Much of this work has pertained to human diseases, largely in the cancer therapy arena. However, considerable research has also been devoted to the nanochemistry for controlling infectious diseases. Among these are ones due to bacterial infections, which can cause serious illnesses leading to death. The onset of multi-drug-resistant (MDR) infections such as those caused by the human pathogen Staphylococcus aureus has created a dearth of problems such as surgical complications, persistent infections, and lack of available treatments. In this article, we set out to review the primary literature on the design and development of new nanoparticle materials for the potential treatment of S. aureus infections, and areas that could be further expanded upon to make nanoparticle antibiotics a mainstay in clinical settings.

Hydrothermal-assisted synthesis of highly crystalline titania-copper oxide binary systems with enhanced antibacterial properties

Binary oxide systems containing TiO₂ and CuO were synthesized using hydrothermal treatment and shown to have enhanced antibacterial properties. A detailed investigation was made of the effect of the molar ratio of components (TiO₂:CuO = 7:3, 5:5, 3:7, 1:9) on the physicochemical parameters and antibacterial activity. Analysis of morphology (SEM, TEM and HRTEM) confirmed the presence of spherical and sheet-shaped particles. On the XRD patterns for the binary oxide materials, two crystalline forms (anatase and monoclinic CuO) were observed. It was found that an increase in CuO content led to a decrease in the BET surface area of the TiO₂-CuO binary oxide systems. The synthesized TiO₂-CuO materials exhibited very good antibacterial activity against both Gram-positive (methicillin-resistant Staphylococcus aureus and Bacillus cereus) and Gram-negative (Salmonella Enteritidis and Pseudomonas aeruginosa) bacteria. The obtained results show that TiO₂-CuO oxide materials may have applications in the biomedical and food industries.

Ca-Ag coexisting nano-structured titania layer on Ti metal surface with enhanced bioactivity, antibacterial and cell compatibility

A nano-structured titanate layer encapsulated with Ca²⁺ and Ag⁺ ions was successfully grown over commercially pure (CP) Ti metal by chemical treatment with H₂O₂ and subsequent treatment with Ca (NO₃)₂/AgNO₃ solutions. Heat treatment at 600 °C, further transformed this nano-structured titanate layer into titania containing Ca²⁺ and Ag⁺ ions. Thus modified Ti metal showed significant enhancement in apatite-forming ability when soaked in simulated body fluid (SBF). Presence of Ag⁺ ions showed good antimicrobial activity against pathogenic Staphylococcus aureus, and, Ca²⁺ ions being a major component of bone mineral accelerated the apatite-forming ability over Ti metal in SBF. Further, Ca²⁺and Ag⁺ ions proportion over Ti metal surface could be optimised in order to have minimum Ag concentration that can have not only antibacterial activity and also cell compatibility against MG 63 osteoblast-like cells. Therefore, the proposed surface modification approach presented here is expected to be useful in orthopaedic implants that necessitate enhanced bioactivity, antibacterial activity and cell compatibility.

Photochemical Surface Modification of Titanium Dioxide Nanotube-Coated Surfaces by Ag-Hydroxyapatite Compositions

Silver-hydroxyapatite coatings prepared from Ag3PO4 microcrystals have been deposited on titanium dioxide nanotubes supported by titanium disks by photodecomposition of predeposited Ag3PO4 microcrystals or their coprecipitate with hydroxyapatite. The SEM-EDS characterization has confirmed excellent film uniformity and consistent deposition over the surface, which is essential for improving osseointegration of tunable antibacterial bone implants.

Bactericidal effects of nanopatterns: A systematic review

We systematically reviewed the currently available evidence on how the design parameters of surface nanopatterns (e.g. height, diameter, and interspacing) relate to their bactericidal behavior. The systematic search of the literature resulted in 46 studies that satisfied the inclusion criteria of examining the bactericidal behavior of nanopatterns with known design parameters in absence of antibacterial agents. Twelve of the included studies also assessed the cytocompatibility of the nanopatterns. Natural and synthetic nanopatterns with a wide range of design parameters were reported in the included studies to exhibit bactericidal behavior. However, most design parameters were in the following ranges: heights of 100-1000 nm, diameters of 10-300 nm, and interspacings of  <500 nm. The most commonly used type of nanopatterns were nanopillars, which could kill bacteria in the following range of design parameters: heights of 100-900 nm, diameters of 20-207 nm, and interspacings of 9-380 nm. The vast majority of the cytocompatibility studies (11 out of 12) showed no adverse effects of bactericidal nanopatterns with the only exception being nanopatterns with extremely high aspect ratios. The paper concludes with a discussion on the evidence available in the literature regarding the killing mechanisms of nanopatterns and the effects of other parameters including surface affinity of bacteria, cell size, and extracellular polymeric substance (EPS) on the killing efficiency. STATEMENT OF SIGNIFICANCE: The use of nanopatterns to kill bacteria without the need for antibiotics represents a rapidly growing area of research. However, the optimum design parameters to maximize the bactericidal behavior of such physical features need to be fully identified. The present manuscript provides a systematic review of the bactericidal nanopatterned surfaces. Identifying the effective range of dimensions in terms of height, diameter, and interspacings, as well as covering their impact on mammalian cells, has enabled a comprehensive discussion including the bactericidal mechanisms and the factors controlling the bactericidal efficiency. Overall, this review helps the readers have a better understanding of the state-of-the-art in the design of bactericidal nanopatterns, serving as a design guideline and contributing to the design of future experimental studies.

A review of nanostructured surfaces and materials for dental implants: surface coating, patterning and functionalization for improved performance

The emerging field of nanostructured implants has enormous scope in the areas of medical science and dental implants. Surface nanofeatures provide significant potential solutions to medical problems by the introduction of better biomaterials, improved implant design, and surface engineering techniques such as coating, patterning, functionalization and molecular grafting at the nanoscale. This review is of an interdisciplinary nature, addressing the history and development of dental implants and the emerging area of nanotechnology in dental implants. After a brief introduction to nanotechnology in dental implants and the main classes of dental implants, an overview of different types of nanomaterials (i.e. metals, metal oxides, ceramics, polymers and hydrides) used in dental implant together with their unique properties, the influence of elemental compositions, and surface morphologies and possible applications are presented from a chemical point of view. In the core of this review, the dental implant materials, physical and chemical fabrication techniques and the role of nanotechnology in achieving ideal dental implants have been discussed. Finally, the critical parameters in dental implant design and available data on the current dental implant surfaces that use nanotopography in clinical dentistry have been discussed.

Methodologies for in vitro and in vivo evaluation of efficacy of antifungal and antibiofilm agents and surface coatings against fungal biofilms

Unlike superficial fungal infections of the skin and nails, which are the most common fungal diseases in humans, invasive fungal infections carry high morbidity and mortality, particularly those associated with biofilm formation on indwelling medical devices. Therapeutic management of these complex diseases is often complicated by the rise in resistance to the commonly used antifungal agents. Therefore, the availability of accurate susceptibility testing methods for determining antifungal resistance, as well as discovery of novel antifungal and antibiofilm agents, are key priorities in medical mycology research. To direct advancements in this field, here we present an overview of the methods currently available for determining (i) the susceptibility or resistance of fungal isolates or biofilms to antifungal or antibiofilm compounds and compound combinations; (ii) the in vivo efficacy of antifungal and antibiofilm compounds and compound combinations; and (iii) the in vitro and in vivo performance of anti-infective coatings and materials to prevent fungal biofilm-based infections.

Potential antibacterial mechanism of silver nanoparticles and the optimization of orthopedic implants by advanced modification technologies

Infection, as a common postoperative complication of orthopedic surgery, is the main reason leading to implant failure. Silver nanoparticles (AgNPs) are considered as a promising antibacterial agent and always used to modify orthopedic implants to prevent infection. To optimize the implants in a reasonable manner, it is critical for us to know the specific antibacterial mechanism, which is still unclear. In this review, we analyzed the potential antibacterial mechanisms of AgNPs, and the influences of AgNPs on osteogenic-related cells, including cellular adhesion, proliferation, and differentiation, were also discussed. In addition, methods to enhance biocompatibility of AgNPs as well as advanced implants modifications technologies were also summarized.

Comparison with the osteoconductivity and bone-bonding ability of the iodine supported titanium, titanium with porous oxide layer and the titanium alloy in the rabbit model

BACKGROUND

One of the serious postoperative complications associated with joint replacement is bacterial infection. In our recent investigations, iodine supported titanium implants demonstrated antibacterial activity in both in vitro and in vivo studies. The surfaces of the implants have porous anodic oxide layer with the antiseptic properties of iodine. According to the literature the titanium with porous anodic oxide have good osteoconductivity. But it is not clear whether the properties of iodine influence bone bonding of implants.

OBJECTIVES

The aim of this study is to evaluate the influence of the properties of iodine and porous anodic oxide layer in the bone bonding ability of titanium implants.

STUDY DESIGN & METHODS

Titanium rods were implanted in intramedullary rabbit femur models, in regard to the cementless hip stem. The implant rods were 5 mm in diameter and 25 mm in length. Three types of titanium rods were implanted.One was untreated titanium (control group (CL)), another was titanium with oxide layer without iodine (oxide layer group (OL)), and the other was Iodine treated Titanium (iodine group (ID)). The rods were inserted into the distal femur. We assessed the bonding strength by a measuring pull-out test at 4, 8, and 12 weeks after implantation. The bone-implant interfaces were evaluated at 4 weeks after implantation.

RESULTS

Pull-out test results of the ID implants were 202, 355, and 344 N, and those of the OL implants were 220, 310, 329 N at 4, 8, and 12 weeks, significantly higher than those of the CL implants (102, 216, and 227 N). But there were no significant difference in ID implants and OL implants. Histological examination revealed that new bone formed on the surface of each types of implants, but significantly more bone made direct contact with the surfaces of the ID implants and OL implants.

CONCLUSIONS

This research showed that new type of coating, iodine coated titanium has low toxicity and good osteoconductivity.

In vitro methods for the evaluation of antimicrobial surface designs

Bacterial adhesion and subsequent biofilm formation on biomedical implants and devices are a major cause of their failure. As systemic antibiotic treatment is often ineffective, there is an urgent need for antimicrobial biomaterials and coatings. The term "antimicrobial" can encompass different mechanisms of action (here termed "antimicrobial surface designs"), such as antimicrobial-releasing, contact-killing or non-adhesivity. Biomaterials equipped with antimicrobial surface designs based on different mechanisms of action require different in vitro evaluation methods. Available industrial standard evaluation tests do not address the specific mechanisms of different antimicrobial surface designs and have therefore been modified over the past years, adding to the myriad of methods available in the literature to evaluate antimicrobial surface designs. The aim of this review is to categorize fourteen presently available methods including industrial standard tests for the in vitro evaluation of antimicrobial surface designs according to their suitability with respect to their antimicrobial mechanism of action. There is no single method or industrial test that allows to distinguish antimicrobial designs according to all three mechanisms identified here. However, critical consideration of each method clearly relates the different methods to a specific mechanism of antimicrobial action. It is anticipated that use of the provided table with the fourteen methods will avoid the use of wrong methods for evaluating new antimicrobial designs and therewith facilitate translation of novel antimicrobial biomaterials and coatings to clinical use. The need for more and better updated industrial standard tests is emphasized.

STATEMENT OF SIGNIFICANCE

European COST-action TD1305, IPROMEDAI aims to provide better understanding of mechanisms of antimicrobial surface designs of biomaterial implants and devices. Current industrial evaluation standard tests do not sufficiently account for different, advanced antimicrobial surface designs, yet are urgently needed to obtain convincing in vitro data for approval of animal experiments and clinical trials. This review aims to provide an innovative and clear guide to choose appropriate evaluation methods for three distinctly different mechanisms of antimicrobial design: (1) antimicrobial-releasing, (2) contact-killing and (3) non-adhesivity. Use of antimicrobial evaluation methods and definition of industrial standard tests, tailored toward the antimicrobial mechanism of the design, as identified here, fulfill a missing link in the translation of novel antimicrobial surface designs to clinical use.

Surface modification of valve metals using plasma electrolytic oxidation for antibacterial applications: A review

Plasma electrolytic oxidation (PEO) is an advance technique to develop porous oxidation layer on light metals, primarily to enhance corrosion and wear resistance. The oxidation layer can also offer a wide variety of mechanical, biomedical, tribological, and antibacterial properties through the incorporation of several ions and particles. Due to the increasing need of antimicrobial surfaces for biomedical implants, antibacterial PEO coatings have been developed through the incorporation of antibacterial agents. Metallic nanoparticles that have been employed most widely as antibacterial agents are reported to demonstrate serious health and environmental threats. To overcome the current limitations of these coatings, there is a significant need to develop antibacterial surfaces that are not harmful for patient's health and environment. Attention of the readers has been directed to utilize bioactive glasses as antibacterial agents for PEO coatings. Bioactive glasses are well known for their excellent bioactivity, biocompatibility, and antibacterial character. PEO coatings incorporated with bioactive glasses can provide environment-friendly antimicrobial surfaces with exceptional bioactivity, biocompatibility, and osseointegration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 590-605, 2018.

Comparison of methods to evaluate bacterial contact-killing materials

Cationic surfaces with alkylated quaternary-ammonium groups kill adhering bacteria upon contact by membrane disruption and are considered increasingly promising as a non-antibiotic based way to eradicate bacteria adhering to surfaces. However, reliable in vitro evaluation methods for bacterial contact-killing surfaces do not yet exist. More importantly, results of different evaluation methods are often conflicting. Therefore, we compared five methods to evaluate contact-killing surfaces. To this end, we have copolymerized quaternary-ammonium groups into diurethane dimethacrylate/glycerol dimethacrylate (UDMA/GDMA) and determined contact-killing efficacies against five different Gram-positive and Gram-negative strains. Spray-coating bacteria from an aerosol onto contact-killing surfaces followed by air-drying as well as ASTM E2149-13a (American Society for Testing and Materials) were found unsuitable, while the Petrifilm® system and JIS Z 2801 (Japanese Industrial Standards) were found to be excellent methods to evaluate bacterial contact-killing surfaces. It is recommended however, that these methods be used in combination with a zone of inhibition on agar assay to exclude that leakage of antimicrobials from the material interferes with the contact-killing ability of the surface.

STATEMENT OF SIGNIFICANCE

Bacterial adhesion to surfaces of biomaterials implants can be life-threatening. Antimicrobials to treat biomaterial-associated infections often fail due to the bacterial biofilm-mode-of-growth or are ineffective due to antibiotic-resistance of causative organisms. Positively-charged, quaternized surfaces can kill bacteria upon contact and are promising as a non-antibiotic-based treatment of biomaterial-associated infections. Reliable methods to determine efficacies of contact-killing surfaces are lacking, however. Here, we show that three out of five methods compared, including an established ASTM, are unsuitable. Methods found suitable should be used in combination with a zone-of-inhibition-assay to establish absence of antimicrobial leaching, potentially interfering with contact-killing. Identification of suitable assays for evaluating bacterial contact-killing will greatly assist this emerging field as an alternative for antibiotic-based treatment of biomaterial-associated-infections.

Antimicrobial Peptides in Biomedical Device Manufacturing

Over the past decades the use of medical devices, such as catheters, artificial heart valves, prosthetic joints, and other implants, has grown significantly. Despite continuous improvements in device design, surgical procedures, and wound care, biomaterial-associated infections (BAI) are still a major problem in modern medicine. Conventional antibiotic treatment often fails due to the low levels of antibiotic at the site of infection. The presence of biofilms on the biomaterial and/or the multidrug-resistant phenotype of the bacteria further impair the efficacy of antibiotic treatment. Removal of the biomaterial is then the last option to control the infection. Clearly, there is a pressing need for alternative strategies to prevent and treat BAI. Synthetic antimicrobial peptides (AMPs) are considered promising candidates as they are active against a broad spectrum of (antibiotic-resistant) planktonic bacteria and biofilms. Moreover, bacteria are less likely to develop resistance to these rapidly-acting peptides. In this review we highlight the four main strategies, three of which applying AMPs, in biomedical device manufacturing to prevent BAI. The first involves modification of the physicochemical characteristics of the surface of implants. Immobilization of AMPs on surfaces of medical devices with a variety of chemical techniques is essential in the second strategy. The main disadvantage of these two strategies relates to the limited antibacterial effect in the tissue surrounding the implant. This limitation is addressed by the third strategy that releases AMPs from a coating in a controlled fashion. Lastly, AMPs can be integrated in the design and manufacturing of additively manufactured/3D-printed implants, owing to the physicochemical characteristics of the implant material and the versatile manufacturing technologies compatible with antimicrobials incorporation. These novel technologies utilizing AMPs will contribute to development of novel and safe antimicrobial medical devices, reducing complications and associated costs of device infection.

Effects of copper nanoparticles in porous TiO2 coatings on bacterial resistance and cytocompatibility of osteoblasts and endothelial cells

Copper (Cu) has garnered increasing interest due to its excellent antimicrobial activity and important roles in human metabolism. Although the biological effects of Cu have been studied, the effects of Cu nanoparticles (NPs) on cell behavior are not well understood. In this study, porous TiO₂ coatings doped with different amounts of Cu NPs (designated as 0 Cu, 0.3 Cu, and 3.0 Cu) are deposited on titanium by micro-arc oxidation (MAO). The Cu NPs coated samples exhibit excellent antibacterial activity against Staphylococcus aureus (S. aureus). In vitro cytocompatibility evaluation discloses that 0 Cu and 0.3 Cu have no toxicity to osteoblasts but 3.0 Cu shows cytotoxicity. 0.3 Cu promotes proliferation and adhesion of osteoblasts and enhances extracellular matrix mineralization (ECM), but has little effects on the alkaline phosphatase activity (ALP) and collagen secretion. Surprisingly, the Cu NPs coated samples show a different behavior with endothelial cells. Both 0.3 Cu and 3.0 Cu show no cytotoxicity on endothelial cells and promote cell proliferation. Production of nitric oxide (NO) and secretion of vascular endothelial growth factor (VEGF) by the endothelial cells are observed from the Cu NPs doped TiO₂ coatings.

Understanding long-term silver release from surface modified porous titanium implants

Prevention of orthopedic device related infection (ODRI) using antibiotics has met with limited amount of success and is still a big concern during post-surgery. As an alternative, use of silver as an antibiotic treatment to prevent surgical infections is being used due to the well-established antimicrobial properties of silver. However, in most cases silver is used in particulate form with wound dressings or with short-term devices such as catheters but not with load-bearing implants. We hypothesize that strongly adherent silver to load-bearing implants can offer longer term solution to infection in vivo. Keeping that in mind, the focus of this study was to understand the long term release study of silver ions for a period of minimum 6months from silver coated surface modified porous titanium implants. Implants were fabricated using a LENS™ system, a powder based additive manufacturing technique, with at least 25% volume porosity, with and without TiO2 nanotubes in phosphate buffer saline (pH 7.4) to see if the total release of silver ions is within the toxic limit for human cells. Considering the fact that infection sites may reduce the local pH, silver release was also studied in acetate buffer (pH 5.0) for a period of 4weeks. Along with that, the osseointegrative properties as well as cytotoxicity of porous titanium implants were assessed in vivo for a period of 12weeks using a rat distal femur model. In vivo results indicate that porous titanium implants with silver coating show comparable, if not better, biocompatibility and bonding at the bone-implant interface negating any concerns related to toxicity related to silver to normal cells. The current research is based on our recently patented technology, however focused on understanding longer-term silver release to mitigate infection related problems in load-bearing implants that can even arise several months after the surgery.

STATEMENT OF SIGNIFICANCE

Prevention of orthopedic device related infection using antibiotics has met with limited success and is still a big concern during post-surgery. Use of silver as an antibiotic treatment to prevent surgical infections is being explored due to the well-established antimicrobial properties of silver. However, in most cases silver is used in particulate form with wound dressings or with short-term devices such as catheters but not with load-bearing implants. We hypothesize that strongly adherent silver to load-bearing implants can offer longer-term solution towards infection in vivo. Keeping that in mind, the focus of this study was to understand the long-term release of silver ions, for a period of minimum 6months, from silver coated surface modified porous titanium implants.

Meglumine antımoniate-TiO2@Ag nanoparticle combinations reduce toxicity of the drug while enhancing its antileishmanial effect

Currently, the treatment of leishmaniasis is increasingly insufficient as current antileishmanial drugs have many disadvantages such as toxic side effects, high cost, and growing drug resistance. In order to overcome these disadvantages, researchers have recently focused on combination therapy by using pentavalent antimonials in conjunction with other antileihmanial compounds. Our previous study found that TiO2@Ag nanoparticles (TiAgNps) demonstrated significant antileishmanial effects. However, a lethal dose of TiAgNps on L. topica promastigotes was found to be toxic for macrophage cells. Moreover, non-toxic concentrations of TiAgNps were ineffective in inhibiting L. topica promastigotes and amastigotes. Thus, we propose the use of TiAgNps in combination with other antileishmanial compounds like meglumine antimoniate (MA) at non-toxic concentrations, which may increase the efficacies of both agents and decrease their toxicities. Therefore, the aim of this study was to determine in vitro and in vivo antileishmanial efficacies of TiAgNps-MA combinations at non-toxic concentrations and develop a new approach for treatment that lowers the toxicities of pentavalent antimonials to minimal levels and enhances their effectiveness. In vitro screening was performed on L. topica promastigote and amastigote-macropage culture by using MTT assay to determine proliferation, perform infection index analysis, and to conduct a Griess reaction for nitric oxide production, while in vivo antileishmanial assays were applied on Balb/c mice with CL models. The results demonstrated that combinations including TiAgNps and MA at non-toxic concentrations were highly efficacious against both promastigotes and amastigotes, while MA application alone did not show any inhibitory effects. It was determined that combination applications decreased the proliferation of L. topica promastigotes 2- to 5-fold in contrast to use of MA alone, and was dependent on concentrations. Moreover, the use of combinations led to inhibition of L. topica amastigotes at rates ranging between 80% and 95%. Additionally, combinations were found to decrease metabolic activities of each form of the parasite at ranges between 7- to 20-fold, causing programmed-cell death and stimulation of macrophages for intensive production of nitric oxide, which is accepted as an important antileishmanial agent (p<0.05). Furthermore, Σ FIC analysis demonstrated that the tested combinations composed little additive, but mostly synergistic effects for inhibition of promastigotes and amastigotes. According to in vivo screening results, the combinations displayed high antileishmanial activities by successfully healing lesions and significantly reducing parasite burdens. Combined, these results show that TiAgNps-MA combinations were much more effective than use of MA alone at non-toxic concentrations and they possess high potential for development of new antileishmanial drugs to fight against leishmaniasis.

Inhibition of biofilm formation on iodine-supported titanium implants

PURPOSE

We have developed iodine-supported titanium implants that suppress microbial activities and conducted in vivo and in vitro studies to determine their antimicrobial properties.

METHODS

The implants were Ti-6Al-4 V titanium implants either untreated (Ti), treated with oxide film on the Ti surface by anodization (Ti-O), or treated with an iodine coating on oxidation film (Ti-I). The strain of bacteria used in this study was Gram-positive Staphylococcus aureus strain ATCC 25923. We analyzed the antibacterial attachment effects in vivo by using rats. The attachment bacteria on the implant surface were evaluated using a spread-plate method assay. A biofilm study was performed in vitro. The biofilm formed after bacterial attachment was qualitatively studied with fluorescence microscopy (FM) and scanning electron microscopy (SEM). Also, the formed biofilm was quantitatively studied with a spread-plate method assay.

RESULTS

In vivo analysis of antimicrobial attachment effects showed that the mean viable bacterial number was significantly lower on Ti-I than Ti or Ti-O surfaces. In the in vitro biofilm study, FM and SEM images showed thick and mature biofilm formation on Ti and Ti-O and thin, small biofilm formation on Ti-I. A quantitative biofilm analysis found a significant difference in the number of viable bacteria between Ti-I and Ti or Ti-O.

CONCLUSIONS

This study showed that iodine-supported implants have a good antibacterial attachment effect and inhibit biofilm formation and growth. Iodine-supported implants may have great potential as innovative antibacterial implants that can prevent implant related infection in orthopaedic surgery.

The controlled drug release by pH-sensitive molecularly imprinted nanospheres for enhanced antibacterial activity

In this study, we prepared pH-sensitive hybrid nanospheres through the implementation of a facile molecularly imprinted polymer (MIP) technique combined with a UV-initiated precipitation polymerization method using vancomycin (VA) for the templates. During the course of this investigation, both 2-hydroxyethyl methacrylate (HEMA) and 2-(diethylamino) ethyl methacrylate (DEAEMA) were utilized as the functional monomers, while ethylene glycol dimethacrylate (EGDMA) was used as a cross-linker. The obtained MIP nanospheres exhibited well-controlled particle size, with a drug loading capacity of about 17%, much higher than that of the non-imprinted polymer (NIP) nanospheres (5%). In addition, the VA loading quantity was closely correlated with the dosage of the cross-linking agent, and the MIP nanospheres exhibited a slower and more controlled VA release rate than the NIP nanospheres. Moreover, these MIP nanospheres were sensitive to pH values, and consequently showed an increasing release rate of VA as the pH level was decreased. The VA-loaded MIP nanospheres showed the higher antibacterial ratio of over 92% against Staphylococcus aureus (S. aureus) while the NIP nanospheres were friendly to S. aureus. These MIP nanospheres can be promising for targeting drug delivery system to achieve specific therapies such as preventing bacterial infections and killing cancer cells without damaging health cells and tissues.

Selective laser melting porous metallic implants with immobilized silver nanoparticles kill and prevent biofilm formation by methicillin-resistant Staphylococcus aureus

Implant-associated infection and limited longevity are two major challenges that orthopedic devices need to simultaneously address. Additively manufactured porous implants have recently shown tremendous promise in improving bone regeneration and osseointegration, but, as any conventional implant, are threatened by infection. In this study, we therefore used rational design and additive manufacturing in the form of selective laser melting (SLM) to fabricate porous titanium implants with interconnected pores, resulting in a 3.75 times larger surface area than corresponding solid implants. The SLM implants were biofunctionalized by embedding silver nanoparticles in an oxide surface layer grown using plasma electrolytic oxidation (PEO) in Ca/P-based electrolytes. The PEO layer of the SLM implants released silver ions for at least 28 days. X-ray diffraction analysis detected hydroxyapatite on the SLM PEO implants but not on the corresponding solid implants. In vitro and ex vivo assays showed strong antimicrobial activity of these novel SLM PEO silver-releasing implants, without any signs of cytotoxicity. The rationally designed SLM porous implants outperformed solid implants with similar dimensions undergoing the same biofunctionalization treatment. This included four times larger amount of released silver ions, two times larger zone of inhibition, and one additional order of magnitude of reduction in numbers of CFU in an ex vivo mouse infection model.